The United States hasn't always had the closest relationship with China or Russia. But give us a few hundred million years, and we could be a lot more unified: A new prediction for the motion of the continents suggests that the Americas and Asia will smoosh together at the north to form the supercontinent dubbed Amasia.

The concept of supercontinents is hardly new. About 300 million years ago, the supercontinent Pangaea included all seven of the continents we now and love today. But the upper part of the Earth's mantle, the rock layer between the crust and the core, is gooey enough to move. As it shifts, so do the tectonic plates above it, causing earthquakes in the short term, and relocating whole continents over millions of years.

The movement of tectonic plates eventually broke up Pangaea about 200 million years ago, just as it had broken up the previous supercontinent, Rodinia, over 500 million years before that. Geologists suspect that supercontinents may form, break up, and reform in cycles that last 500 to 700 million years. If so, then what supercontinent will cover Earth's surface in the future, and where will it be?

A new paper in Nature states that Amasia will form, as others have suggested previously, but the researchers have settled on a new theory for where it will be based on their new model, "orthoversion."

The authors wrote:

"Two hypotheses have been proposed for the organizing pattern of successive supercontinents. ‘Introversion' is the model whereby the relatively young, interior ocean stops spreading and closes such that a successor supercontinent forms where its predecessor was located. ‘Extroversion' is the model in which the relatively old, exterior ocean closes completely, such that a successor supercontinent forms in the hemisphere opposite to that of its predecessor. A third model, which we call ‘orthoversion', predicts that a successor supercontinent forms… orthogonal to the centroid of its predecessor."

If introversion occurs, then the relatively young Atlantic Ocean will close up and Amasia will form where Pangaea once sat. If the theory of extroversion wins out, then the Pacific Ocean will close and Amasia will settle down in Rodinia's old place, across the planet from Pangaea's former location. But according this new orthoversion model, Amasia's location will be at a right angle from both Pangaea and Rodinia: at the North Pole. During its formation, Amasia will close up the Arctic Ocean and the Caribbean Sea.

But don't count on Amasia just yet. Other theories predict that the continents will form a second Pangaea — dubbed Novopangaea, Pangaea Ultima or Pangaea Proxima. At least the geologists have plenty of time to figure it out, before it actually happens.